The present invention is related to drydocks for the repair of ships. More specifically, the present invention relates to drydocks that are simple to maintain and are inexpensive.
Drydocks are used to repair ships. The five conventional methods of docking ships are:
(1) graving docks, (2) floating drydocks, (3) marine railways, (4) vertical lifts, and (5) travel lifts on rubber wheels.
A graving dock is a fixed basin constructed of reinforced concrete or granite walls and floors. With the use of steel or concrete gates (caissons), the basins can be dewatered to accommodate a ship to be repaired in dry conditions. The problem with graving docks is that the excavation in the construction of graving docks are expensive, time consuming, and complex, particularly in seismic areas. The flooding, dewatering, and drainage systems including the pump house are expensive to construct and difficult to operate and maintain. Entrance of a ship into a graving dock is extremely difficult. It requires detailed elaborate procedures, the experience of a certified dock master, and the assistance of a large crew. The flooding and dewatering process are time consuming.
Floating docks are essentially floating basins constructed of reinforced concrete or steel which can be flooded or dewatered to receive a ship to be repaired in dry condition. The disadvantage of floating drydocks is that special attention is required to the stability of this system and the selection of the appropriate mooring system. Except for the excavation, the limitations and disadvantages of these drydocks are similar to the graving docks.
A marine railway is an inclined plane system in gear hauling machinery which is able to pull a cradle and a ship out of the water. The disadvantage of marine railways are that these systems are limited to small classes of ships. (Approximately 5,000 long tons maximum loading capacity). They are more subject to mishap than other docking facilities and vulnerable to earthquake forces. Since they are made of structural steel and are exposed to the salt water environment, they are subjected to severe corrosion.
A vertical lift is an elevator system which lifts the ship vertically out of the water. The problem with vertical lifts are that they have limited lifting capacity, are vulnerable to earthquake forces and are very expensive to build.
Lastly, a travel lift on rubber wheels is a steel frame system with a hoist with small lifting capacity. The problem with travel lifts on rubber wheels for small boats, is that they are very limited in their lifting capacity and are used for only small pleasure boats.